Liquid feeding apparatus



LIQUID FEEDING APPARATUS Filed May 24, 1954 INVHVTOR.

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nited States Patent 2,759,764 LIQUID FEEDING APPARATUS Robert C. Juvinall and William L. Smart, Indianapolis, ind, assignors to Ransburg Electra-Coating Corps, In dianapolis, Ind., a corporation of Indiana Application May 24, 1954, Serial No. 431,742

6 Claims. (Cl. 299 -63) Numerous industrial processes require that a liquid be fed with a downward com onent from one stationary member to another moving member without appreciable loss or leakage of the liquid from its desired downward path of flow. For example, in the electrostatic spray coating of articles of manufacture it has been found particularly desirable to feed liquid coating material from a stationary reservoir to a rotating atomizing device such as a flat disc or flaring bell for atomization therefrom and electrostatic deposition on the articles. in certain coating arrangements it is necessary to feed such atomizing devices by means of a generally vertical hollow shaft axially aflixed above the rotating device so that the liquid coating material will flow downwardly along the inner wall of the shaft to be uniformly spread over a surface of the rotating device.

It is well known that certain liquid coating materials, particularly some pigmented paints, have extremely abrasive qualities and that on exposure to air most liquid coating materials leave a gummy residue. Moreover,

liquid coating materials generally contain solvents which readily attack the materials used in conventional liquid sealing devices. These qualities make the useful life of conventional sealing devices very short. Once the liquid coating material leaks past its seal, its abrasive and gummy qualities will quickly render the bearing structure and other moving parts to the rotating atomizi'ng device unserviceable. For this reason it is desirable in feeding liquid coating material so such a device that conventional mechanical seals and related packings be eliminated.

In feeding liquid coating material downwardly through a rotating hollow shaft to the surface of an atomizihg device care must be taken that drops [of liquid do not drip or fall free of the feeding device through the hol low shaft onto the article being coated. This requires proper design of the feed tube and proper arrangement between the stationary feed tube and the inner wall of the rotating shaft. i

Our invention is directed to providing means for feeding liquid for downward flow through a hollow rotating shaft to the surface of an atomizing device or the like without using conventional packin-gs or liquid sealing devices. We have discovered that liquid can be fed downwardly without dripping to a rotating hollow shaft by a downwardly presented stationary feed tube extending a substantial distance into the rotating hollow shaft with its lower portion smoothly curved toward the inner wall of the shaft and terminating in a sharp edge closely adjacent the inner wall. The lower terminus of the stationary feed tube, to provide superior liquid transference, should lie closer to the inner wall of the shaft than any other portion of the feed tube and the end of the tube should be spaced less than .05 inch from the wall of the shaftand preferably not more than .015 inch especially at low liquid deliveries.

An object of our invention is to provide improvements in the protection of the bearing structure and other moving parts of a rotatable hollow shaft. Another object is to provide a more etfic'ient means for feeding liquid through a rotating hollow shaft.

Means for accomplishing the above stated and related objects of our invention will now be described in detail with reference to the accompanying drawings in which:

Fig. 1 is a partially broken away el'evational view of an atomizing device for use in an electrostatic coating system embodying our invention; and V Fig. 2 is a detailed view of the stationary feed tube shown in Fig. 1.

Our invention is admirably adapted for use with an atom'izin'g device for spray coating but the invention may assume many different forms and the above mentioned drawings and the following description should be understood as merely illustrative of the principles of the invention. The scope of the invention is not limited to the following description.

Referring new to Fig. 1 there is shown an annularedg'ed atomizing device 10 which includes an atomizing disc 11 on the lower end of a rotatable hollow shaft 12. The disc and shaft are rotated by an integral motor as sembly lying within housing 13 whose details are not shown as our invention is independent of the motor or other driving means for draft 12 and disc 11.

Shaft 12 e'it'tends axially through the major portion of housing 13. Lying above the upper end of rotatable shaft 12 is a stationary tube support 15 having an axial passageway concentric with shaft 12. A stationary feed tube 16 having a lower terminus 16a is mounted concentrically within the passageway of stationary tube support 15 by means of a set screw 18 and sealed by an (i -ring 19. one to the close tolerances involved terminus 16a should be securely emplaced in relation to the inner wall of shaft 12 and to this end set screw 18 is located to bear against the middleof the upper collar of tube 16 with a substantial area of the collar snugly fitted against tube support 15 both above and below the set screw.

A back plate 21) having an axial passageway communieating with stationary feed tube 16 is securely mounted on the upper end of stationary tube support 15. Liquid coating material is fed at a controlled rate by a line 21 from a reservoir 22 through the passageway in back plate 20 to the interior of feed tube 16. Atomizing device 10 may be maintained at a high electrical potential by connection to a high voltage source 24 as shown or other means known to the art employed to efiect a partide-depositing potential difference between the atomized coating material and the articles. This is generally accomplished by maintaining the articles and their supports at a diiference of potential from the atomizer, preferably by grounding the articles and maintaining the atomizer at high voltage as shown. v

Fig. 2 is adetailed view of stationary feed tube 16 with its lower portion shown in cross section. At its upper end and along its major portion tube 16 is concentric with tube support 15 and rotating shaft 122. in order to bring the liquid coat ng material close to the inner wall of the rotating shaft for transfer from stationary feed tube 16 to notating shaft 12 in a smooth uniform flow and without the formation of liquid drops which might fall free from the end of tube 16 through the shaft, it was found desirable to bend the lower end of the feed tube to bring it within .05 inch of the inner wall of the shaft. To prevent undesirable turbulence in the liquid flow through tube 16 a gradual smooth curvature at the lower end of the feed tube was made. The curvature should be such that terminus 16a will constitute the lowermost portion a of the feed tube. Preferably a tangent to the outer surface of terminus 16a makes an angle of substantially less than 90 with the axis of shaft 12.

In bringing the lower end of the feed tube close to the inner wall of the shaft, additional problems are encountered in that close spacing between the entire open face or mouth of the feed tube and the inner wall of the shaft will cause undesirable squirting of the liquid. Also if the area of the feed tube lying closely adjacent the shaft is large it interferes with liquid transference and literally wipes off liquid already on the inner wall of the shaft onto the stationary feed tube from which it may drip off. To prevent such squirting and wiping off the open face of the feed tube may be concavely dished or otherwise made to form a sharp edged lower projection which would lie closer to the inner wall of the shaft than any other portion of the feed tube. This lower projection will support the liquid flowing to the inner shaft wall and yet present a minimum area of feed tube close to the shaft. It was further found that the best liquid transference from the stationary to the rotating member took place when the edge of the terminus of the feed tube was relatively sharp.

It should be noted that it is not necessary shaft 12 be exactly or even substantially vertical. The axis of the shaft must only have some downward component. But if the shaft is inclined from the vertical, the terminus 16a of the feed tube should be positioned adjacent the lower side of the inner wall of the shaft so that terminus 16a is the lowermost portion of the feed tube.

One commonly used atomizing device which incorporates our invention employes a rotating hollow shaft having an inner diameter of approximately .75 inch. Various coating operations carried on with such an atomizing device require liquid to be fed at deliveries of from 15 to 900 cubic centimeters per minute. The device may be rotated at speeds of from several hundred to several thousand revolutions per minute. A tube constructed in the form of stationary feed tube 16 was found to feed liquid coating material to the inner wall of the hollow shaft at deliveries and speeds within the above ranges and to effect onto the wall of the rotating shaft without dripping liquid transference smoothly or splashing.

When used with a hollow shaft having an inner diameter of .75 inch, the inner diameter of feed tube 16 was approximately .25 inch with its lower end uniformly curved with a radius of curvature of approximately 2.15 inches. The lower extremity of the feed tube had a sharp edge spaced less than .05 inch from the inner wall of the shaft. The sharp edge of the tube was formed by grinding the open face of the tube substantially flat so that the open face of the tube which formed the sharp edge made an angle of approximately 15 to the axis of the hollow shaft and the lower end of the feed tube was closer to the inner wall of the shaft than was any other portion of the feed tube.

We claim:

1. A liquid feeding device comprising a rotatable hollow shaft whose axis has a vertical component, an annular-edged atomizer mounted on the lower end of said shaft, said atomizer having an extended lower surface and a passageway concentric with the axis of said shaft leading from the inner wall of the said shaft to the lower surface of said atomizer, a downwardly presented stationary feed tube lying within said hollow shaft and having a sharp-edged lower terminus lying closer to the inner wall of said shaft than any other portion of the feed tube and spaced less than .05 inch from said inner wall, means for rotating said shaft and atomizer about their axis, and means for feeding liquid down said feed tube to its sharpedged terminus for flow onto the inner wall of said shaft and thence down said inner wall to the lower surface of said atomizer.

2. A liquid feeding device comprising an annular-edged atomizer having a rotatable hollow shaft whose axis has a vertical component, a stationary feed tube whose open lower end lies within the hollow shaft of said atomizer and terminates in a sharp-edged projection spaced less than .05 inch from the inner wall of said shaft, the open lower end of said feed tube making a substantial angle with the axis of said shaft, means for rotating said atomizer about its axis, and means for feeding liquid through said feed tube to be discharged from its lower end onto the rotating inner wall of said shaft for flow to the annular edge of said atomizer.

3. Apparatus as set forth in claim 2 wherein the lower portion of said feed tube is curved and its open face concavely dished to form the sharp-edged projection at the lower end of said feed tube whereby said projection lies closer to the inner Wall of said shaft than does any other portion of said feed tube.

4. A liquid feeding device comprising an atomizer mounted for rotation about a generally vertical axis, said atomizer having an inner liquid-guiding surface concentric about said vertical axis, a downwardly presented stationary feed tube whose lower portion lies surrounded by the inner surface of said atomizer, the lower portion of said feed tube having a lowermost terminus closely adjacent the inner surface of the atomizer, and the lower portion of said feed tube being uniformly curved to make an angle of substantially less than between a tangent to the lower terminus of the feed tube and the axis of said atomizer, means for rotating said atomizer about its axis, and means for feeding liquid downwardly through said feed tube and over its lowermost terminus onto the rotating liquid-guiding surface of said atomizer.

5. A liquid feeding device comprising a downwardly disposed rotatable hollow shaft, said shaft having an inner diameter of approximately .75 inch; an annular-edged atomizer mounted on the lower end of said hollow shaft; a stationary feed tube having an inner diameter of approximately .25 inch which, except for its lower end, lies concentric with said hollow shaft, the lower end of said feed tube being uniformly curved with a radius of curvature of approximately 2.15 inches, the lower extremity of said feed tube having a sharp edge closely adjacent the inner wall of said shaft, and the open face of the tube making said edge being at an angle of approximately 15 to the axis of said hollow shaft; means for rotating said shaft and atomizer about their axis; and means for feeding liquid downwardly through said feed tube onto the rotating surface of said shaft.

61 Apparatus as set forth in claim 5 wherein the sharp edge of the feed tube is spaced less than .05 inch from the inner wall of the shaft.

Henriksen Oct. 22, 1940 Hoogendam Oct. 4, 1949 

2. A LIQUID FEEDING DEVICE COMPRISING AN ANNULAR-EDGED ATOMIZER HAVING A ROTATABLE HOLLOW SHAFT WHOSE AXIS HAS A VERTICAL COMPONENT, A STATIONARY FEED TUBE WHOSE OPEN LOWER END LIES WITHIN THE HOLLOW SHAFT OF SAID ATOMIZER AND TERMINATES IN SHARP-EDGED PROJECTION SPACED LESS THAN .05 INCH FROM THE INNER WALL OF SAID SHAFT, THE OPEN LOWER END OF SAID FEED TUBE MAKING A SUBSTANTIAL ANGLE WITH THE AXIS OF SAID SHAFT, MEANS FOR ROTATING SAID ATOMIZER ABOUT ITS AXIS, AND MEANS FOR FEEDING LIQUID THROUGH SAID FEED TUBE TO BE DISCHARGED FROM ITS LOWER END ONTO THE ROTATING INNER WALL OF SAID SHAFT FOR FLOW TO THE ANNULAR EDGE OF SAID ATOMIZER. 